Technical Abstract:
Soil resources can be heterogeneously distributed, both horizontally and vertically, and management can affect levels and distributions. In November 2003, we initiated a study examining how total N, total C, and organic matter in soils of 1.6 ha experimental paddocks (n=4) were spatially distributed following 27 years of sustained management. Included were intensively and extensively grazed native prairie, heavily grazed winter wheat under conservation tillage, and unmanaged relict prairie. Soil cores (n=100) to 100 cm depth were collected (where possible) at 1.5 m intervals along 150 m transects situated between a ridge and toe slope common to all paddocks. Cores were sectioned and bulk density determined; data from 0-5 cm, 5-10 cm and 10-25 cm are reported. Concentration of total soil C, N and organic matter were predicted from equations developed (n=165) by relating key wavelengths from near infrared reflectance spectroscopy scans to laboratory-determined values by partial least squares regression. Spatial distributions and patch structures (concentration and pool scales) were described by split moving windows. Equations for C and N had R^2>0.97 while equations for organic matter had R^2=0.87. Distributions were highly variable within paddocks, with extremes regularly separated by <10 m distance, and management affected concentration and pool-scale measurements. The native paddocks had higher concentrations than the wheat paddock, and 0-5 cm sections had the highest levels within all paddocks. Pool-scale measures were less definitive due to higher bulk densities in the intensively grazed native and wheat paddocks. Additional studies on the spatial distribution of soil resources are required.